The invention is directed to an improved device for detecting faulty operation of a heat pump system. Specifically, this invention employs a comparison of the actual run time with the expected percent run time for the heat pump system being monitored.
The expected percent run time of a heat pump system with a known capacity is a function of the outside ambient air temperature and the heat loss of the enclosed space for which the temperature is to be maintained. As the outdoor ambient air temperature decreases, there will be an increase in the heat loss of the enclosed space. This combination will translate into an increase in the percent run time of the heat pump along with a decrease in its effective output. An auxiliary heat unit is normally provided to compensate for the difference between the heat loss of the enclosed space and the output of the heat pump at temperatures below a "balance point", that is, where the heat loss of the enclosed space is equivalent to the output of the heat pump.
A degradation in the efficiency of operation of the heat pump system will be reflected in an increase in the actual percent run time of the heat pump for a specified outdoor ambient air temperature, and a corresponding elevation in the balance point temperature. An increase in the actual percent run time of the heat pump results in its own higher energy consumption and an elevation of the balance point temperature results in greater use of the auxiliary heat which has a relatively higher rate of energy consumption. Unfortunately, until an abnormally high energy bill is received, the user is normally unable to detect when there is degradation in the efficiency of operation of a heat pump system since the temperature in the enclosed space will still be maintained.
Therefore, it is beneficial to equip a heat pump system with monitoring apparatus which will alert a user to a decrease in efficiency, thus allowing the user to minimize the use of the more expensive auxiliary heat by recognizing and correcting the problem as soon as it occurs. There is currently no effective available device for alerting the user to a decrease in efficiency of operation of a heat pump system over a wide ambient air temperature range. Previous devices have centered on monitoring a heat pump in relation to its balance point. However, those devices prove to be of limited value since the user will only be alerted to a decrease in efficiency should the auxiliary heat be activated above the expected balance point. Thus, with such devices, an inefficiently operating heat pump will not be detected while ambient air temperatures remain sufficiently above the balance point temperature so that the auxiliary heat is not activated.
An object of this invention is to provide monitoring apparatus for a heat pump system which will detect abnormal increases in the actual percent run time by monitoring the actual run time of the heat pump, the run time of the auxiliary heat, and the outdoor ambient air temperature over a fixed period of time.
A second object of this invention is to provide for a comparison of the expected percent run time for the average outdoor temperature measured and for the heat loss of the enclosed space with the actual percent run time and to provide an alarm signal when the heat pump system fails to operate within the expected parameters.
The apparatus of this invention is comprised of means for sensing the actual run time of the compressor of a heat pump system during a predetermined test time interval, means for sensing the average outdoor temperature during the test time interval, means for storing the expected run time for the compressor, means for comparing the actual run time with the stored expected run time and means for automatically providing an indication when the actual run time exceeds the expected run time.
The method of this invention involves the steps of sensing the actual run time of the compressor of a heat pump system during a predetermined test time interval, sensing the average outdoor temperature during the test time interval, storing the expected run time for the compressor, comparing the actual run time with the stored expected run time and automatically providing an indication when the actual run time exceeds the expected run time.